1. Field of the Invention
This invention relates generally to semiconductor manufacturing, and, more particularly, to a method and apparatus for performing dynamic sampling of semiconductor wafers in a production line.
2. Description of the Related Art
The technology explosion in the manufacturing industry has resulted in many new and innovative manufacturing processes. Today""s manufacturing processes, particularly semiconductor manufacturing processes, call for a large number of important steps. These process steps are usually vital, and, therefore, require a number of inputs that are generally fine-tuned to maintain proper manufacturing control.
The manufacture of semiconductor devices requires a number of discrete process steps to create a packaged semiconductor device from raw semiconductor material. The various processes, from the initial growth of the semiconductor material, the slicing of the semiconductor crystal into individual wafers, the fabrication stages (etching, doping, ion implanting, or the like), to the packaging and final testing of the completed device, are so different from one another and specialized that the processes may be performed in different manufacturing locations that contain different control schemes.
Among the factors that affect semiconductor device manufacturing are wafer-to-wafer variations that are caused by manufacturing problems that include effects of manufacturing machine tool variations, memory effects of manufacturing chambers, first-wafer effects, and the like. Among the process steps that are adversely affected by such factors are photolithography overlay processes, etching processes, and rapid thermal anneal (RTA) processes. Overlay is one of several important steps in the photolithography area of semiconductor manufacturing. Overlay control involves measuring the misalignment between two successive patterned layers on the surface of a semiconductor device. Generally, minimizing misalignment errors helps to ensure that the multiple layers of the semiconductor devices are connected and functional. As technology facilitates smaller critical dimensions for semiconductor devices, the need for reducing misalignment errors increases dramatically.
Generally, photolithography engineers currently analyze the overlay errors a few times a month. The results from the analysis of the overlay errors are used to make updates to exposure tool settings manually. Some of the problems associated with the current methods include the fact that the exposure tool settings are only updated a few times a month. Furthermore, currently, the exposure tool updates are commonly performed manually.
Generally, a set of processing steps is performed on a lot of wafers on a semiconductor manufacturing tool called an exposure tool or a stepper. The manufacturing tool communicates with a manufacturing framework or a network of processing modules. The manufacturing tool is generally connected to an equipment interface. The equipment interface is connected to a machine interface to which the stepper is connected, thereby facilitating communications between the stepper and the manufacturing framework. The machine interface can generally be part of an advanced process control (APC) system. The APC system initiates a control script, which can be a software program that automatically retrieves the data needed to execute a manufacturing process. The input parameters that control the manufacturing process are revised periodically in a manual fashion. As the need for higher precision manufacturing processes are required, improved methods are needed to revise input parameters that control manufacturing processes in a more automated and timely manner. Furthermore, wafer-to-wafer manufacturing variations can cause non-uniform quality of semiconductor devices.
In order to perform corrections to the manufacturing processes, such as revising the input parameters that control the manufacturing processes, manufacturing or production data is acquired. Generally, manufacturing data is acquired using a variety of production data acquisition tools, such as metrology tools. One problem associated with acquiring production data is that manufacturing costs increase without a substantial contribution to the actual production process itself.
A known technique for evaluating the acceptability of the semiconductor manufacturing processes, particularly in photolithography processes, involves measuring critical dimensions and other parameters after the photoresist has been developed. One method used to evaluate the developed wafer is to use scatterometry to generate an intensity measurement indicative of the pattern on the wafer. Other production data acquisition methods, such as measuring critical dimensions and the like, can be employed to acquire production data and make adjustments to manufacturing processes. Currently, the industry lacks an efficient means for acquiring production data to make adjustments to production processes in a cost-effective manner.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
In one aspect of the present invention, a method is provided for performing dynamic sampling of a production line. A first plurality of semiconductor wafers are processed. A minimum sampling rate of semiconductor wafers is calculated. Wafers from the first plurality of semiconductor wafers are selected and analyzed at the calculated sampling rate. The performance of the processing of the first plurality of semiconductor wafers is quantified, based upon the analyzed wafers. A dynamic sampling process is performed based upon the quantification of the performance of the processing of semiconductor wafers.
In another aspect of the present invention, an apparatus is provided for performing dynamic sampling of a production line. The apparatus of the present invention comprises: a computer system; a manufacturing model coupled with said computer system, said manufacturing model being capable of generating and modifying at least one control input parameter signal; a machine interface coupled with said manufacturing model, said machine interface being capable of receiving process recipes from said manufacturing model; a processing tool capable of processing semiconductor wafers and coupled with said machine interface, said first processing tool being capable of receiving at least one control input parameter signal from said machine interface; a metrology tool coupled with said first processing tool and said second processing tool, said metrology tool being capable of acquiring metrology data; a metrology data processing unit coupled with said metrology, said metrology data processing unit being capable of organizing said acquired metrology data; and a sample rate adjustment unit coupled with said computer system, said sample rate adjustment unit being capable of determining a sampling rate for selecting and sampling processed semiconductor wafers based upon said organized metrology data.